Nightly Slack Publish contains Deleted Benchmarks

[stanbrub]

The query that the nightly slack notification is derived from contains at least one benchmark that no longer exists. It certainly is possible that some long-standing benchmarks no longer exist or have been replaced by better ones (as in the case of parquet). Need to account for that.

Static_Benchmark                               Chng5d  Var5d     Rate  ChngRls  ScrProb
ParquetWrite- GZIP 2 Strs 2 Longs 2 Dbls...   -0.2030   0.3%  954,608    -1.6%     0.0%

• Nighty queries are based in part on past days. Ensure inclusion of only benchmarks that have measurements for the latest day
• Care must be taken not to eliminate previous days for legitimate benchmark names
• The latest benchmarks are not necessarily the benchmarks from the day the nightly queries are run
  • If a nightly build fails, no benchmark data is pushed to GCloud for that day
  • That would make the latest benchmarks yesterday's benchmark list